Articles comprising a release liner having a high coefficient of friction and good roll stability

ABSTRACT

The present invention relates to articles comprising a substrate, a release liner and an adhesive layer sandwiched between the substrate and release liner and methods of manufacturing such articles. The release liner has a relatively high coefficient of friction and has shrinkage properties that are substantially the same as or greater than the substrate. The article exhibits good roll stability, being substantially free of defects when supplied in a roll form.

FIELD OF THE INVENTION

[0001] The present invention relates to articles comprising a substrate,a release liner and an adhesive layer sandwiched between the substrateand release liner and methods of manufacturing such articles. Therelease liner has a relatively high coefficient of friction and hasshrinkage properties that are substantially the same as or greater thanthe substrate. The article exhibits good roll stability, beingsubstantially free of defects when supplied in a roll form.

BACKGROUND OF THE INVENTION

[0002] A variety of articles, such as tapes (e.g. packaging, automotive,medical), labels, sheeting for traffic control signage, and commercialgraphic films for advertising and promotional displays comprise anadhesive coated substrate (eg. backing, sheeting) having a release linertemporarily covering the adhesive layer. These articled are typicallysupplied as sheets or in a roll form. Provided that proper tensioning isemployed, it is typically unproblematic to convert dimensionally stablesubstrates in combination with dimensionally stable release liners.

[0003] On the other hand, flexible plastic substrates tend to be muchmore difficult to convert, often exhibiting roll defects such aswrinkles and buckling. Many of these defects occur during themanufacturing process and are primarily process related. Other defects,appear after manufacturing and prior to use and thus are relatedprimarily to the physical properties of the materials employed as afunction of storage conditions as well as interactions of thesematerials with each other.

[0004] WO 99/14281 relates to a release liner for use with a pressuresensitive adhesive. The release liner includes a film of a thermoplasticelastomeric olefin. At p. 14, this reference states that “The releaseliner of the invention preferably exhibits substantially no shrinking orbuckling when brought to room temperature after being exposed to anelevated temperature for an extended period of time. A preferred linerexhibits substantially no shrinking or buckling when brought to roomtemperature (i.e., about 20-25° C.) after being exposed to a temperatureof about 90° C., more preferably about 120° C., and most preferablyabout 150° C., for a period of about one-half hour, more preferablyabout one hour. Shrinking and buckling can be avoided by selecting arelease liner having thermal expansion and contraction coefficientssubstantially similar to those of the intended substrate.”

[0005] It is generally known and appreciated by those of ordinary skillin the art that a combination of substrate, adhesive and release linerthat exhibits good roll stability can exhibit roll defects uponreplacing either the substrate or the liner with a different material.For example, “Scotchlite High Intensity Grade Reflective Sheeting Series3870”, commercially available from Minnesota, Mining and ManufacturingCompany (“3M”), St. Paul, Minn. employs an “encapsulated lens” typeretroreflective sheeting, generally prepared as described in U.S. Pat.No 4,025,159. This sheeting employs a polymethylmethacrylate cover filmin combination with a thermally crosslinked adhesive and a release linerhaving a relatively low coefficient of friction. Although thiscombination of substrate, adhesive, and liner exhibits good rollstability, roll defects became evident in attempting to replace theliner with an alternative material.

SUMMARY OF THE INVENTION

[0006] The present inventors have discovered that “shrinkage” is animportant factor in preventing roll defects that occurpost-manufacturing during storage. Accordingly, an object of the presentinvention is to provide an article comprising an adhesive sandwichedbetween a substrate and release liner that exhibits good roll stability.Another object of the invention is to provide a retroreflective articlecomprising an adhesive sandwiched between a substrate and release linerwherein the article or the adhesive in combination with the liner can besubjected to electron beam radiant energy and maintain sufficiently lowrelease values.

[0007] In one aspect, the present invention is an article comprising anadhesive layer disposed between a substrate and a liner. The liner isreleasably adhered to the adhesive and has a relatively high coefficientof friction, of at least about 0.30. The substrate exhibits shrinkageand the liner exhibits a shrinkage ranging from substantially the sameas to greater than the substrate.

[0008] The coefficient of friction of the liner is preferably at leastabout 0.40, more preferably at least about 0.45, and most preferably atleast about 0.50.

[0009] The substrate is preferably a film comprising acrylic, poly(vinylchloride), poly(vinyl fluoride), polyurethane, polyolefin, polyester,and combinations thereof with acrylic such as polymethymethacrylate andpolyolefin being most preferred.

[0010] The force per unit width of the substrate is preferably at leasttwo to three times greater than the liner. In preferred embodiments theforce per unit width of the substrate is at least 1×10³ Newtons/cmgreater and more preferably 1×10⁴ Newtons/cm greater than the liner.

[0011] The adhesive is preferably heat-stable and preferably crosslinkedsuch as acrylate based pressure sensitive adhesive compositions. Thepreferred adhesive compositions are crosslinked with an electron beamradiant energy source and thus are substantially free of photoinitiator.

[0012] The substrate is preferably retroreflective sheeting such asenclosed-lens, encapsulated lens, and cube-corner type retroreflectivesheeting with encapsulated lens type being most preferred.

[0013] The release liner preferably comprises a backing and a releasecoating composition comprising a cure-on-demand moisture curablecomposition having reactive silane functionality. The moisture-curablerelease composition comprises a compound comprising molecules bearingreactive silane functional groups and an acid generating material thatis free of ammonium salt.

[0014] In another aspect, the invention provides an article comprisingan adhesive layer disposed between a retroreflective substrate and aliner, wherein the adhesive-facing surface of the liner has acoefficient of friction of at least about 0.30.

[0015] In another aspect, the present invention is a method of making anarticle comprising:

[0016] a) providing a substrate that exhibits shrinkage;

[0017] b) providing a liner that exhibits shrinkage ranging fromsubstantially the same as the substrate to greater than the substrateand a coefficient of friction of greater than 0.30;

[0018] c) coating the substrate with an adhesive composition;

[0019] d) contacting the liner to the adhesive composition forming anarticle; and

[0020] e) winding the article into a roll.

[0021] In another aspect, the method of making the article comprises:

[0022] a) providing a substrate that exhibits shrinkage;

[0023] b) providing a liner that exhibits shrinkage ranging fromsubstantially the same as the substrate to greater than the substrateand a coefficient of friction of greater than 0.30;

[0024] c) coating the liner with an adhesive composition;

[0025] d) contacting the substrate to the adhesive composition formingan article; and

[0026] e) winding the article into a roll.

[0027] In another aspect, the method of making the article comprises:

[0028] a) providing a substrate that exhibits shrinkage;

[0029] b) providing a first liner;

[0030] c) coating the first liner with an adhesive composition;

[0031] d) contacting the substrate to the adhesive composition;

[0032] e) stripping the first liner exposing the adhesive;

[0033] f) contacting the adhesive to a second liner that exhibitsshrinkage ranging from substantially the same as the substrate togreater than the substrate and a coefficient of friction of greater than0.30 forming an article; and

[0034] e) winding the article into a roll.

[0035] Each of these methods preferably further comprise exposing theadhesive to an electron beam energy source.

DESCRIPTION OF THE DRAWINGS

[0036]FIG. 1 depicts the thermal expansion of various liners incomparison to an adhesive coated substrate, “Sheeting 3870”. The thermalexpansion was measured using a Dynamic Mechanical Analysis (DMA)technique, as described in further detail in the forthcoming examples.Since the thermal expansion of the release liner is a function of therelease liner backing, the thermal expansion of Liner 1 and Liner 2 isthe same since these two liners have the same backing and only differwith regard to the release coating composition as well as thecoefficient of friction of the release coating. FIG. 1 illustrates thatLiner 4 and Liner 6 exhibit thermal expansion most similar to that ofthe substrate (Sheeting 3870 with adhesive), whereas Liners 1 and 2,exhibit a thermal expansion less similar to the substrate.

[0037]FIGS. 2 and 3 depict the shrinkage of Liners 1 and 2, Liner 5 andLiner 6 in comparison to an adhesive coated substrate, “Sheeting 3870”.In FIG. 2, the shrinkage was measured using another Dynamic MechanicalAnalysis (DMA) technique, as described in further detail in theforthcoming examples. In FIG. 3, the shrinkage was measured using alaser interferometer and a ball slide stage, as described in furtherdetail in the forthcoming examples. FIG. 2 depicts shrinkage at aconstant temperature over a shorter duration of time, ranging up to 1200minutes, whereas FIG. 3 depicts the shrinkage at a constant temperatureover a longer time span, up to 60 days. Both figures depict that Liner 1and 2 exhibit shrinkage substantially greater than the adhesive coatedsubstrate (“Sheeting 3870”), whereas Liner 5 and Liner 6 exhibit lessshrinkage than the substrate.

DETAILED DESCRIPTION OF THE DRAWINGS

[0038] The present invention relates to an article comprising asubstrate, an adhesive, and a release liner. The adhesive is sandwichedbetween the substrate and the liner. The adhesive is typically pressuresensitive or alternatively lacks cohesive strength. For instanceswherein the adhesive is pressure sensitive, the release linerfacilitates handling, prevents contamination, and insures that theadhesive substantially maintains its intended adhesive properties. Theliner is typically left in contact with the adhesive layer while thearticle is being converted, packaged and shipped to the end-user (e.g.sign manufacturer). The liner is then removed from the adhesive layerand the adhesive coated substrate is bonded to a “target substrate”,such as a sign backing, billboard, automobile, truck, airplane,building, awning, window, floor, etc. For instances wherein the adhesivelacks cohesive strength, such as in the case of adhesive compositionsthat are subsequently cured or crosslinked, the liner may providedimensional stability to the adhesive prior to curing. Alternatively, orin addition thereto, the liner may provide dimensional stability to thesubstrate, the substrate being formed in-line by curing of a substrateprecursor composition.

[0039] As used herein the terminology, “substrate” refers to a sheet orfilm that is capable of being wound around a 3 inch (7.6 cm) core byhand into a roll-form without cracking. The substrate typically rangesin thickness from about 0.01 mm to about 2 mm.

[0040] “Adhesive” refers to a material that is capable of beingpermanently bonded to the substrate and releasably bonded to the liner.“Permanently bonded” means that the adhesive can not be easilyphysically removed at ambient temperature (25° C.) without damaging thesubstrate. “Releasably bonded” refers to the ability to cleanly removethe liner from the adhesive without tearing or otherwise damaging theliner, the adhesive layer, or the substrate. The force of removal istypically less than about 400 g/2.5 cm and preferably less than about200 g/2.5 cm as measured according to ASTM D3330/3330M, Test Method A,Volume 15.09, Summary 1.1.1.

[0041] “Liner” and “release liner” are used interchangeably and refer toa sheet or film having at least one surface that is capable of beingreleasably bonded to the adhesive, as previously described. In the caseof double-faced tape, both surfaces of the liner are releasably bondedto the adhesive layer.

[0042] The articles of the invention have two major exposed surfaces,the substrate surface and the release liner surface. The substratesurface is also the “viewing surface” in the case of retroreflectivesheeting, commercial graphic films, etc. The adhesive is typicallypermanently bonded to the surface of the substrate opposing the viewingsurface. The surface of the adhesive opposing the surface bonded to thesubstrate is releasably bonded to the liner.

[0043] The substrate, adhesive and release liner are chosen such thatthe combination of such exhibit good roll stability, being substantiallyfree of defects. As used herein “good roll stability” refers to rollsexhibiting a rating less than “3” when prepared by hand and testedaccording to the Roll Stability test at 120° F. (49° C.) for 10 days, asdescribed in further detail in the forthcoming examples. The articlespreferably exhibit good roll stability at 120° F. (49° C.) for anextended duration of time, exhibiting a rating ranging from “1” to “2”at 120° F. (49° C.) for 22 days and longer. Typically, however, the rollstability at 10 days is predictive of the roll stability at the sametemperature for longer duration of times. Most preferably, the articlesof the present invention exhibit good roll stability at higher storagetemperatures ranging up to about 150° F. (66° C.).

[0044] Unlike many dimensionally stable materials, the substrate of thepresent invention is preferably comprised of a material or mixture ofmaterials such that the substrate as a whole exhibits shrinkage. As usedherein, “shrinkage” refers to a sheet or film that exhibits a (1−L/LO)of greater than 0.05% at 10 days according to Shrinkage Test B, asdescribed in further detail in the forthcoming examples. In the absenceof the present invention, the severity of roll defects tends to increasewith increasing shrinkage, wherein the substrate exhibits a shrinkage ofgreater than about 0.1%, greater than about 0.2%, and greater than about0.4%. However, in general the shrinkage of the substrate is typicallyless than about 5% and more typically less than about 2%.

[0045] Shrinkage is different from thermal expansion. Whereas, thermalexpansion and contraction is generally reversible at least at lowertemperatures; shrinkage is irreversible, a function of time andprevalent at lower temperatures, such as evident during storage.

[0046] The liner is chosen such that it exhibits substantially the sameas or greater shrinkage than the substrate. The physical properties ofthe liner backing, rather than the release coating, typically dominatethe overall physical properties of the liner. As used herein,“substantially the same shrinkage” refers to the difference in shrinkagebetween the liner and substrate divided by the shrinkage of thesubstrate is greater than −0.1 based on Shrinkage Test B (10 days at120° F. [49°]). Further, the present invention provides good rollstability wherein the difference in shrinkage between the liner andsubstrate divided by the shrinkage of the substrate is greater thanabout 0, greater than about 1 and greater than 2.

[0047] In general, as the modulus of the liner increases, the importanceof shrinkage to roll stability increases. Good roll stability can alsobe achieved by using a low modulus liner. Low modulus liners oftenexhibit a greater amount of creep in comparison to a higher modulusliner and thus, can more easily accommodate the shrinkage of thesubstrate without the formation of visible roll defects.

[0048] The substrate is substantially stronger in comparison to theliner. The force per unit width, as measured according to ASTM D-882(using a gap of 25 cm, a sample width of 1 inch (2.5 cm) and a rate of2.5 cm/min), tends to be a useful physical property for comparing therelative strength of the substrate to the liner. The force per linealinch (2.5 cm) of the substrate (e.g. single film, multi-layer film,retroreflective sheeting) tends to range from about 1×10³ Newtons/cm toabout 1×10⁶ Newtons/cm. At a lower force per unit width, the substratetends to stretch or distort during manufacturing or the substrate cantear upon removal of the liner, whereas at a higher force per unit widththe substrate tends to be too stiff to be wound into a roll at preferredsubstrate film thicknesses of less than 10 mils (250 microns).

[0049] The force per unit width of the liner tends to be several ordersof magnitude lower than the substrate. In general, the force per unitwidth of the substrate is at least two to three times greater than theliner. In preferred embodiments the force per unit width of thesubstrate is at least 1×10³ Newtons/cm greater and preferably 1×10⁴Newtons/cm greater than the liner. If however, one were to use a linerhaving approximately the same force per unit width as the substrate, theliner should be chosen such that it exhibits substantially the sameshrinkage as the substrate.

[0050] Since the adhesive layer of the article tends to be the “weakestlink”, the physical properties of the adhesive, such as shrinkage, havesubstantially no effect on roll stability in view of the adhesive havinglower strength in comparison to both the substrate and liner. Theadhesive tends to yield to accommodate the shrinkage of either thesubstrate and/or liner. Accordingly, the shrinkage of the substrate isequal-to the shrinkage of an adhesive coated substrate, per FIGS. 2 and3. If, however, a highly crosslinked adhesive were employed, theshrinkage of the adhesive would become increasingly important. In suchinstances, the Applicants surmise that it would be important to selectan adhesive having shrinkage properties substantially the same as theliner and/or substrate.

[0051] In addition to the requisite shrinkage, the release liner ischosen such that the surface that is in contact with the adhesive has arelatively high coefficient of friction. The coefficient of friction, asmeasured according to ASTM D 1894-63, subprocedure A, as described infurther detail in the forthcoming examples, is at least about 0.30.Further, the coefficient of friction is generally less than about 2. Thecoefficient of friction is preferably at least about 0.40, morepreferably at least about 0.45, and most preferably at least about 0.50.The Applicants have found that release liners having a relatively lowcoefficient of friction exhibit too high of a release in instanceswherein the release liner in combination with the adhesive were exposedto an electron beam (EB) radiant energy source. EB is often used incuring processes of either the substrate and/or the adhesive to buildthe tensile or cohesive strength of such materials. Further, EB is alsoused to sterilize materials such as bandages and medical tapes.Materials (e.g. adhesive, substrate precursor compositions) that are EBcured, rather than UV cured are typically substantially free ofphotoinitiator, having less than 0.1% photoinitiator present aftercuring.

[0052] Provided that the substrate exhibits shrinkage, as previouslydescribed, a wide variety of materials are suitable for use as thesubstrate in the article of the invention including various filmscomprised of thermoplastic polymeric materials. Such thermoplasticmaterials may comprise reactive groups that crosslink duringmanufacturing by means of heat (i.e. thermosetting) or a radiant energysource (ultraviolet [UV], EB). The films are typically nonporous.However, microporous, apertured, as well as materials further comprisingwater-absorbing particles such as silica and/or super-absorbentpolymers, may also be employed. Other suitable substrates include wovenand nonwoven fabrics.

[0053] Representative examples of polymeric materials (e.g. sheet,films) for use as the substrate in the invention includeacrylic-containing films (e.g. poly(methyl) methacrylate [PMMA],copolymers and terpolymers of PMMA), poly(vinyl chloride)-containingfilms, (e.g., vinyl, polymeric materialized vinyl, reinforced vinyl,vinyl/acrylic blends, plasticized vinyl), poly(vinyl fluoride)containing films, urethane-containing films, polyolefin-containing filmsand polyester-containing films. Further, the substrate may comprisecopolymers of such polymeric species. In particular, films comprisingPMMA and polyolefin are especially prone to shrinkage.

[0054] The shrinkage of the substrate is dependent on the composition ofthe substrate as well as the method of manufacture and manufacturingconditions (e.g. temperature). Accordingly, films prepared from the samecompositions may vary in shrinkage depending on the processingconditions such as temperature, quench rate, etc.

[0055] Depending on the intended end use, the substrates for use in theinvention may be clear, translucent, or opaque. Additionally, thesubstrate may be transmissive, reflective, or retroreflective.

[0056] The substrate may be a single film, a multi-layer film, or acomposite of one or more film layer(s) in combination with othermaterials such as adhesive layers, color layers, etc. A preferredsubstrate for use in the invention is retroreflective sheeting. The twomost common types of retroreflective sheeting are microsphere-basedsheeting and cube corner-based sheeting. Microsphere sheeting, sometimesreferred to as “beaded sheeting,” is well known to the art and includesa multitude of microspheres typically at least partially embedded in abinder layer, and associated specular or diffuse reflecting materials(such as metallic vapor or sputter coatings, metal flakes, or pigmentparticles). “Enclosed-lens” based sheeting refers to retroreflectivesheeting in which the beads are in spaced relationship to the reflectorbut in full contact with resin. The “encapsulated lens” retroreflectivesheeting is designed such that the reflector is in direct contact withthe bead but the opposite side of the bead is in a gas interface.Illustrative examples of microsphere-based sheeting are disclosed inU.S. Pat. Nos. 4,025,159 (McGrath); 4,983,436 (Bailey); 5,064,272(Bailey); 5,066,098 (Kult); 5,069,964 (Tolliver); and 5,262,225(Wilson).

[0057] Cube corner sheeting, sometimes referred to as prismatic,microprismatic, triple mirror or total internal reflection sheetings,typically include a multitude of cube corner elements to retroreflectincident light. Cube corner retroreflectors typically include a sheethaving a generally planar front surface and an array of cube cornerelements protruding from the back surface. Cube corner reflectingelements include generally trihedral structures that have threeapproximately mutually perpendicular lateral faces meeting in a singlecorner—a cube corner. In use, the retroreflector is arranged with thefront surface disposed generally toward the anticipated location ofintended observers and the light source. Light incident on the frontsurface enters the sheet and passes through the body of the sheet to bereflected by each of the three faces of the elements, so as to exit thefront surface in a direction substantially toward the light source. Inthe case of total internal reflection, the air interface must remainfree of dirt, water and adhesive and therefore is enclosed by a sealingfilm. The light rays are typically reflected at the lateral faces due tototal internal reflection, or by reflective coatings, as previouslydescribed, on the back side of the lateral faces. Preferred polymers forcube corner sheeting include poly(carbonate), poly(methyl methacrylate),poly(ethylene terephthalate), aliphatic polyurethanes, as well asethylene copolymers and ionomers thereof. Cube corner sheeting may beprepared by casting directly onto a film, such as described in U.S. Pat.No. 5,691,846 (Benson, Jr.) incorporated herein by reference. Preferredpolymers for radiation cured cube corners include cross-linked acrylatessuch as multifunctional acrylates or epoxies and acrylated urethanesblended with mono-and multifunctional monomers. Further, cube cornerssuch as those previously described may be cast on to plasticizedpolyvinyl chloride film for more flexible cast cube corner sheeting.These polymers are preferred for one or more reasons including thermalstability, environmental stability, clarity, excellent release from thetooling or mold, and capability of receiving a reflective coating.

[0058] In embodiments wherein the sheeting is likely to be exposed tomoisture, the cube corner retroreflective elements are preferablyencapsulated with a seal film. In instances wherein cube corner sheetingis employed as the retroreflective layer, a backing layer may be presentfor the purpose of opacifying the article or article, improving thescratch and gouge resistance thereof, and/or eliminating the blockingtendencies of the seal film. Illustrative examples of cube corner-basedretroreflective sheeting are disclosed in U.S. Pat. Nos. 5,138,488(Szczech); 5,387,458 (Pavelka); 5,450,235 (Smith); 5,605,761 (Burns);5,614,286 (Bacon Jr.) and 5,691,846 (Benson, Jr.).

[0059] The coefficient of retroreflection of the retroreflective layervaries depending on the desired properties of the finished article. Ingeneral, however, the retroreflective layer typically has a coefficientof retroreflection ranging from about 5 candelas per lux per squaremeter, for colored retroreflective layers, to about 1500 candelas perlux per square meter at 0.2 degree observation angle and −4 degreeentrance angle, as measured according to ASTM E-810 test method forcoefficient of retroreflection of retroreflective sheeting. For cubecorner sheeting the coefficient of retroreflection is preferably atleast about 200 candelas per lux per square meter for fluorescent orangeand at least about 550 candelas per lux per square meter for white. ForType I white sheetings (“engineering grade”), the minimum coefficient ofretroreflection is 70 cd/fc/ft², whereas for Type III white sheetings(“high intensity”) the minimum coefficient of retroreflection is 250cd/fc/ft².

[0060] In a preferred embodiment the substrate is a retroreflectivesheeting comprising polymethylmethacrylate, either as a cover film on anencapsulated lens type sheeting or as the retroreflective layer of acube corner type retroreflective sheeting.

[0061] In general and in particular for commercial graphic films, thesubstrate may further comprise an image reception layer (e.g. inkreceptive layer). The image reception layer may be disposed on theexposed surface of the viewing surface of the article. Alternatively,the image reception layer may be buried in the construction, beingdisposed on the unexposed surface of a cover film. In such instances theimage reception layer of the cover film is typically reverse imagedprior to being bonded to the viewing surface. A preferred imagereception layer comprising an acid- or acid/acrylate modified ethylenevinyl acetate resin, as disclosed in U.S. Pat. No. 5,721,086 (Emslanderet al.). The image reception layer comprises a polymer comprising atleast two monoethylenically unsaturated monomeric units, wherein onemonomeric unit comprises a substituted alkene where each branchcomprises from 0 to about 8 carbon atoms and wherein one other monomericunit comprises a (meth)acrylic acid ester of a nontertiary alkyl alcoholin which the alkyl group contains from 1 to about 12 carbon atoms andcan include heteroatoms in the alkyl chain and in which the alcohol canbe linear, branched, or cyclic in nature.

[0062] Commercially available films, suitable for use as the substrate,include a multitude of films typically used for signage and commercialgraphic uses such as available from 3M under the trade designations of“Panaflex”, “Nomad”, “Scotchcal”, “Scotchlite”, “Controltac”, and“Controltac Plus”.

[0063] A wide variety of adhesive compositions are suitable for use inthe invention. The adhesive composition is preferably pressuresensitive. Various pressure sensitive adhesives are known in the art andare described in the patent literature. Representativepressure-sensitive adhesive compositions include compositions based onacrylate or acrylics, natural rubber, tackified block copolymers,polyvinyl acetate, ethylene vinyl acetate, polyesters, polyurethanes,silicones, etc., as well as themosetting adhesives such as epoxyacrylate and epoxy polyesters.

[0064] The adhesive is preferably heat-stable such as acrylate pressuresensitive adhesives described in Re 24906 (Ulrich); U.S. Pat. Nos.4,181,752 (Martens et al.) 4,818,610 (Zimmerman et al.) and 5,804,610(Hamer) as well as silicone pressure sensitive adhesive. Preferredadhesive compositions for use with retroreflective substrates includeadhesive compositions described in U.S. Pat. No. 5,861,211 (Thakkar), WO95/26281 (Thakkar) and WO 98/17466 (Thakker), incorporated herein byreference.

[0065] The adhesive can be prepared by any of the known methodsincluding emulsion polymerization, solvent polymerization, as well assolventless polymerization. Typically acrylate adhesives comprisehomopolymers and copolymers of monofunctional unsaturated acrylic ormethacrylic acid ester monomer of non-tertiary alcohols having fromabout 1 to about 20 carbon atoms, and preferably from about 4 to 12carbon atoms. A comonomer may be optionally included to improve thestrength of the adhesive. Such reinforcing comonomers typically have ahigher homopolymer glass transition temperature than the acrylic acidester homopolymer.

[0066] Suitable acrylic acid ester monomer include 2-ethylhexylacrylate, isooctyl acrylate, isononyl acrylate, n-butyl acrylate, decylacrylate, dodecyl acrylate, octadecyl acrylate, and mixtures thereof.Useful reinforcing comonomers include acrylic acid methacrylic acid,itaconic acid, acrylamide, substituted acrylamines, N-vinyl pyrrolidone,N-vinyl caprolactam, isobornyl acrylate, and cyclohexyl acrylate.

[0067] The surface of the adhesive layer opposing the surface bonded tothe substrate is releasably adhered to a liner. The liner typicallycomprises a backing and a release coating composition coated on thesurface of the backing that is in contact with the adhesive. The backingis typically a sheet or film comprised of a thermoplastic material suchas those previously described with regard to the substrate. Although thecomposition of the substrate and the liner backing may be the same, theliner is typically a different material, that is substantially weaker instrength than the substrate, as previously described. A preferred linerbacking for use with PMMA substrate is a polyolefin, such as apolypropylene copolymer. The thickness of the backing generally rangesfrom about 10 microns to 300 microns.

[0068] A release coating is generally provided as a continuous surfacelayer at a thickness ranging from 0.1 micron to 3 microns.Alternatively, the liner may be comprised of a backing material thatprovides the requisite release properties in the absence of a releasecoating.

[0069] The liner (i.e. liner backing) exhibits shrinkage that issubstantially the same as or greater than the substrate as well as has arelatively high coefficient of friction, as previously described. Eventhough the release liner has a relatively high coefficient of friction,the level of release is still relatively low. The release of the liner,as measured according to ASTM D3330/3330M, Test Method A, (Volume 15.09,Summary 1.1.1) is less than about 200 g/2.5 cm and greater than about 10g/2.5 cm. Preferably the release of liner is less than about 150 g/2.5cm, more preferably less than about 100 g/2.5 cm, even more preferablyless than about 75 g/2.5 cm, and even more preferably about 50 g/2.5 cmor less. The release liner typically has a release of at least about 10g/2.5 cm to insure the release liner does not fall off prior to removalby the end user.

[0070] The crosslink density of the silicone network is one of thefactors which affect the release characteristics of a given silicone. Ingeneral, the higher the crosslink density of the silicone, the lower therelease force. (Handbook of Pressure Sensitive Adhesive Technology,Donatas Satas, Satas & Associates, 1999, pp. 655) Crosslink density canbe determined by degree of polymerization (DP) or repeating unitsbetween crosslinks which is calculated by the average molecular weightdivided by the product of the number of crosslinking functionalities perchain multiplied by the molecular weight of the repeating unit.

[0071] Siloxane coatings with a high crosslink density exhibit a highcoefficient of friction (COF) while siloxane coatings with a lowcrosslink density tend to exhibit a low coefficient of friction (COF).The coefficient of friction is also related to the thickness, surfacemorphology and method of application. Whereas previously employedrelease liners for use with retroreflective substrates tend to have acoefficient of friction of less than about 0.25 and a correspondingtheoretical degree of polymerization of about 5000 or greater, thepreferred release liner compositions of the present invention typicallyhave a theoretical degree of polymerization of less than 3500, morepreferably less than 1000, and even more preferably less than 500.

[0072] A wide variety of release coatings compositions are known and aresuitable for use in the invention provided that such coating provide therequisite coefficient of friction and release. Release coatingcompositions generally comprise low surface energy materials such aspolyethylene, polypropylene, fluorocarbons, silicone and combinationthereof are known. For example, epoxy silicones are disclosed in U.S.Pat. Nos. 4,822,687 (Kessel et al.), 5,217,805 (Kessel et al.),5,576,356 (Kessel et al., 5,332,797 (Kessel et al.); perfluoropolyethersare disclosed in U.S. Pat. No. 4,830,910 (Larson), fluorocarbons in apolymer matrix are disclosed in U.S. Pat. No. 5,110,667 (Galick et al.)and various types of silicones are described in U.S. Pat. Nos. 2,588,367(Dennett), 3,960,810 (Chandra et al.), 4,162,356 (Grenoble), 4,306,050(Koerner et al.); British Patent No. 1,375,792, (Colquhoun et al.), andGerman Patent No. 2,736,499 (Hockemeyer), each of which is incorporatedherein by reference.

[0073] Further, commercially available release coating compositions areavailable from various suppliers such as General Electric Co. (Albany,N.Y.), Dow Corning under the SYL-OFF tradename, (Midland, Mich.), WackerChemie (Germany), and Th. Goldschmidt AC (Germany). Coatings arecommercially available from Akrosil (Menasha, Wis.), and Loparex(Willowbrook, Ill.).

[0074] A preferred release coating is a cure-on-demand moisture curablecomposition comprising molecules bearing reactive silane functionalgroups and an acid generating material that is preferably free ofammonium salt, as described in U.S. Pat. No. 6,204,350, incorporatedherein by reference. Preferably, the reactive silane functional groupsare the only acid curable groups present in the composition.

[0075] The preferred release coatings comprise polydimethyl siloxane(PDMS), crosslinker, and photo acid generator.

[0076] The preferred polydimethyl siloxane comprises silanol terminatedPDMS [HO (SiMe₂O)_(n)SiMe₂OH] with a relatively low molecular weight.The preferred molecular weight ranges from about 200 to 5000 g/mole withabout 300 to 2000 g/mole being more preferred. The most preferredmolecular weight range in 400 to 1500 g/mole.

[0077] Crosslinkers include molecules bearing reactive silane functionalgroups which may be represented by the following structure:

[0078] wherein moiety A is an m-valent radical selected from fluoroalkylradicals, fluoroaryl radicals, and polymeric radicals comprising apolymer selected from polysiloxane, polyolefin, polyester,polyphosphazene, fluorosilicone, fluorinated polyacrylate, fluorinatedpolyether, fluorinated polyester, and derivatives and combinationsthereof;

[0079] p is an integer from 1 to 3;

[0080] m is an integer greater than or equal to 1;

[0081] each R¹ is individually selected from alkyl radicals and acylradicals;

[0082] each R² is individually selected from hydrogen, alkyl radicals,acyl radicals and aryl radicals; and

[0083] G is an optional linking moiety which, when present, linksradical A to the reactive silane functional groups.

[0084] The reactive silane groups typically comprise a silicon atombonded to one or more acyloxy or alkoxy groups. The average reactivesilane functionality of the moisture curable composition is greater than2 so as to form a crosslinked network upon curing.

[0085] The preferred crosslinkers include alkoxy silane containingsilicones and alkoxy silane containing saturated olefins. The mostpreferred crosslinkers comprise bisalkoxysilyl alkanes, generalrepresented by following structures:

(RO)_(m)Me_(3-m)Si(CH₂)_(n)SiMe_(3-m)(OR)_(m)

[0086] A wide variety of acid generating materials can be used in thepractice of the invention to catalyze the moisture curing reaction,including onium salts such as sulfonium and iodonium salts. Activatingthe acid generating material liberates an acid that initiates andaccelerates crosslinking of the moisture-curable composition through theformation of Si—O—Si crosslinks. Activation may be accomplished byirradiating the composition with, for example, ultraviolet, visiblelight, EB or microwave radiation. While heat may be used to activate theacid generating material, the compositions of the inventionadvantageously do not require this and thereby can avoid undesirabledamage to heat sensitive substrates.

[0087] Other release coating compositions that also would be expected toexhibit the desired COF based on the theoretical degree ofpolymerization include solventless platinum silicone.

[0088] The articles of the invention can be prepared with any of avariety of known methods. The adhesive is either coated directly ontothe substrate or coated directly onto the liner. The substrate and linerare most commonly provided as pre-manufactured roll-goods.Alternatively, the substrate or liner may be made in-line by coating asubstrate or liner pre-cursor composition onto a release coated belt,roller, etc. By “precursor composition”, it is meant that thecomposition is substantially weaker in strength in comparison to itsstrength in the finished article, the finished article being thesubstrate/adhesive/liner composite. For example, the pre-cursorcomposition may be an extruded thermoplastic material that merelyrequires cooling to sufficiently build in strength and/or a materialthat is crosslinked or cured by means of a chemical reaction induced byheat, moisture or radiant energy. In addition, rather than applying theadhesive directly to the substrate, the adhesive may first be applied toan intermediate material, such as a release coated roller orintermediate liner, and then transfer coated onto the substrate or linerof the article.

[0089] The articles of the invention comprising an adhesive sandwichedbetween a substrate and a release liner may be finished products or anintermediate. The release liner is removed and the pressure sensitiveadhesive coated surface of the substrate is applied to a target surface.For various retroreflective uses, the target surface is often a barrel,cone, post, roadway, license plate, barricade, or sign backing. In thecase of commercial graphics films, the substrate is typically imaged andapplied to a building, automobile, airplane etc. Further, the inventionfinds utility for various tapes and label (e.g. packaging, automotive,medical) that employ substrates that exhibit shrinkage.

EXAMPLES

[0090] Objects and advantages of the invention are further illustratedby the following examples, but the particular materials and amountsthereof recited in the examples, as well as other conditions anddetails, should not be construed to unduly limit the invention. Allpercentages and ratios herein are by weight unless otherwise specified.

[0091] Test Methods Used in the Examples

[0092] Coefficient of Friction (“COF”)

[0093] The Coefficient of Friction of release coatings was determinedusing a Slip/Peel Tester commercially available from IMASS, Inc., Accord(Hingham), Mass. (“IMASS”) under the trade designations “ModelSP-102B-3M90” and “Model SP-2000” and following the procedure based onASTM D 1894-63, subprocedure A. An approximately 25×15 cm (10×6 inch)area of release-coated backings was adhered to the platform of theSlip/Peel. Tester such that the release-coated surface was exposed. Carewas taken to insure that the release-coated surface was untouched,uncontaminated, flat, and free of wrinkles. Both the release surface andfriction sled (wrapped with 3.2 mm thick medium density foam rubber,commercially available from IMASS under the trade designation “ModelSP-101038”) were blown with compressed air to remove any loose debris.The friction sled was placed on the release-coated surface, and thechain attached to the sled was affixed to the force transducer of theSlip/Peel Tester. The platform of the Slip/Peel Tester was set in motionat a speed of 15 cm/min (6 in/min), thereby dragging the friction sledacross the release-coated surface. The instrument calculated andreported the average kinetic friction force, omitting the staticfriction force. The kinetic coefficient of friction was obtained bydividing the kinetic friction force by the weight of the friction sled.

[0094] Thermal Expansion

[0095] Thermal Expansion of samples was measured using a DynamicMechanical Analyzer commercially available from Perkin-ElmerCorporation, Norwalk, Conn. under the trade designation “Model DMA-7e”.Each sample was cut such that it was approximately 5.5 mm wide in thetransverse (i.e., cross web) direction by 2.5 cm long in the machinedirection (with respect to the direction the substrate or liner wasmanufactured). The sample was tested in the machine direction with anapplied load of 8.8 Newtons per meter (N/m; 0.05 lb./lineal inch). Asthe sample was being tested, the temperature was increased from about18° C. to 60° C. at a rate of 1° C. per minute.

[0096] Shrinkage

“Shrinkage Test Method A”

[0097] The amount of shrinkage occurring on samples initially at roomtemperature (about 20° C.) and then subjected to 68° C. (154° F.) forabout 1200 minutes was measured. The samples were prepared as describedfor the Thermal Expansion Test method. Each sample was tested in themachine direction using the Perkin-Elmer Model DMA-7e Analyzer with anapplied load of 8.8 N/m. Each sample was held for 1 hour at 18° C., atwhich time the temperature was increased to 68° C. at a rate of 0.5° C.per minute, and then held at 68° C. for 1200 minutes.

“Shrinkage Test Method B”

[0098] The amount of shrinkage occurring on samples was measured using alaser interferometer and a ball slide stage. Each sample was cut suchthat it was approximately 2.5 cm wide in the transverse direction by 30cm long in the machine direction. Each sample was tested in the machinedirection (with respect to how the substrate was manufactured) byaccurately measuring the sample length and then subjecting the sample to66° C. (150° F.) for the specified amount of time and then measuring thelength of the sample.

[0099] Roll Stability

[0100] Roll stability was evaluated by visual inspection of articles inroll form. A liner/adhesive/ substrate construction was formed bylaminating a liner to the adhesive side of adhesive-coated reflectivesheeting. Rolls were prepared by either hand wrapping or machinewrapping each construction around a cardboard core of about 3 inches(7.6 cm) diameter with the liner on the inside of the roll. Theconstruction was cut, and the outer wrap was taped to the roll tomaintain a tightly wrapped roll.

[0101] For the hand wrapped rolls, constructions of about 1 meter wideby 3 meters long in the machine direction were tightly hand wrappedaround the core in machine direction with respect to the direction thesubstrate was manufactured. For machine wrapped rolls, constructions ofabout 1 meter wide by about 10 to 25 meters in length in the machinedirection were wrapped onto the core by first mounting the constructionon the unwind end of a rewind machine. The construction was thenthreaded through the machine, taped to the core on the winder spindle atthe opposite end of the machine and wound in the machine direction ontothe core.

[0102] The wrapped rolls were stored in various test environments forvarious amounts of time. The test conditions used were 150° F. (66° C.)oven for 24 hours (“150”); 120° F. (49° C.) oven for 3, 10 or 22 days(“120/3; 120/10; 120/22”) or 90° F. (32° C.)/90% relative humidity for34 days (“90/90”).

[0103] The rolls were removed from the test environment and allowed toequilibrate at room temperature, unwrapped, inspected and rated forgeneral appearance and wrinkling. Visual defects of each construction onthe side of the liner adjacent the adhesive were rated from 1 to 5 asdescribed below:

[0104] 1. Smooth; no defects.

[0105] 2. Slight roughness; no wrinkles.

[0106] 3. Very rough; “golf ball” appearance beginning to form.

[0107] 4. Distinct golf ball effect; several individual cells havedistorted; minor wrinkle may be starting to form.

[0108] 5. Several individual cells have distorted; adjacent cells havedistorted to form small wrinkles; large wrinkles can be seen in someareas.

[0109] Release

“Release Test Method A”

[0110] Peel force was performed on constructions of about 2.5 cm wide byabout 20 cm long. Each liner/adhesive/polyolefin film construction wasadhered to a 7 cm wide by 28 cm long aluminum panel (6061T6 alloy withetch and desmut surface from Q Panel Company, Cleveland, Ohio) usingdouble sided adhesive tape. The exposed adhesive of the double sidedtape was placed on the aluminum panel and laminated to the panel byrunning a rubber coated, 5 cm wide roller back and forth along thelength of the adhesive strip twice using hand pressure. The releaseliner was removed from the double sided tape and the polyolefin filmside of the liner/adhesive/polyolefin film construction was laminated tothe double sided tape on the test panel using a rubber roller asdetailed above. The aluminum panel was clamped on the sliding stagewhich was clamped in the lower jaw of a Sintech 1 Tensile Testingapparatus commercially available from MTS, Eden Prairie, Minn. About 5cm of the liner was peeled back from the liner/adhesive/polyolefin filmconstruction and clamped in the upper jaw of the tensile testingapparatus. The liner was separated from the adhesive of theliner/adhesive/polyolefin film construction at a 90 degree peel angleusing a crosshead speed of 30 cm/minute. The peel force was recorded ingrams/2.5 cm over a length of at least 10 cm and the average peel forcewas obtained for 3 replicates.

“Release Test Method B”

[0111] The release values were measured according to ASTM D3330/3330M,Test Method A, Volume 15.09, Summary 1.1.1. TABLE I Liners Used in theExamples Liner Description of Release Liner COF 1 Liner on “ScotchliteHigh Intensity Grade 0.12 Reflective Sheeting Series 3870”, commerciallyavailable from 3M in the USA, having a polyolefin backing and a linerthickness of 3 mils (0.076 mm)  2* Liner on “Scotchlite High Intensity0.51 Grade Reflective Sheeting Series 3870”, commercially available from3M in the USA, except the release coating was replaced with the siliconecoating described below (polyolefin backing, 3 mils) 3 “Nat 3.0; HDSilox H1K/0”, commercially — available from International Paper AkrosilDivision, Menasha, WI, having a high density polyethylene backing and aliner thickness of 3 mils (0.076 mm) 4 “PET 1-2 PESTR(NAT) 8000A(1N)”, —commercially available from DCP-Lohja Inc., Willowbrook, IL, having apolyethylene terephthalate backing and a liner thickness of 2 mils (0.05mm) 5 Liner on reflective sheeting commercially 0.53 available from 3Munder the trade designation “Scotchlite Diamond Grade VIP ReflectiveSheeting Series 3990” commercially available from 3M in the USA, havinga polyolefin backing and a liner thickness of 3.2 mils (0.081 mm) 6Liner on “Scotchlite High Intensity Grade — Reflective Sheeting Series3870”, commercially available from 3M in Europe, having a polyolefinbacking and a liner thickness of 3 mils (0.076 mm)

[0112] The chill rolls had the temperatures of 50° F.(10° C.), 150°F.(66° C.), and 150° F.(66° C.), respectively with each roll having adiameter of 17.75 inches(45 cm). The backing was treated with air coronato achieve a surface energy on the order of 40-60 dynes/cm. The treatedsurface was further coated with the solution of 85 parts of silanolterminated PDMS, 15 parts of bistriethoxysilyloctane, and 2 parts ofdodecylphenyl iodonium hexafluoroantimonate in a 80/20 blend of heptaneand methyl ethyl ketone. The solution was applied by a gravure coaterand dried in an air flotation oven to a dry coating weight ofapproximately 0.7 g/m². The release coating was cured by passing undermedium pressure mercury lamps with an exposure energy of between 15 and20 mJ/cm².

Examples 1-4 and Comparative Examples A-D

[0113] Examples 1-4 and Comparative Examples A-D were prepared using“Scotchlite High Intensity Grade Reflective Sheeting Series 3870”commercially available from 3M in the USA without the adhesive or lineras the substrate, referred to as “Sheeting 3870” hereafter in theexamples unless specified otherwise. An adhesive and the liner of TABLEI, as indicated by Table II, were laminated to Sheeting 3870 usingeither a “Liner Exchange” method or a “Direct Coat” method.

[0114] When the direct coat method was used, a solventless, tackifiedacrylate adhesive was coated onto the liner at a thickness of 0.08 mm (3mils). The adhesive was cured using an EB apparatus commerciallyavailable from Energy Sciences, Inc., Wilmington, Mass. under the tradedesignation “Electrocure Series” (System 7961, Model EC300/134/400) witha dosage of 8 Mrads at 200 Kev. The adhesive-coated liner and Sheeting3870 were fed through two nip rollers to laminate the adhesive to thesheeting.

[0115] When the liner exchange method was used, a solvent-based,tackified acrylate adhesive was coated onto a silicone coated papercarrier web at an adhesive coating thickness of about 3 mils (75microns). The adhesive-coated liner was run through a four zone oven(Zone 1=250-260° F. [121° C.-127° C.], Zone 2=300-315° F. [149° C.-157°C.], Zone 3=350-355° F. [177° C.-179° C.], Zone 4 heat off) at a rate ofabout 15 meters per minute to remove the solvent and thermally crosslinkthe adhesive. The adhesive-coated carrier web and the sheeting were fedthrough two nip rollers to laminate the adhesive-coated carrier web tothe sheeting. The carrier web was then removed from the laminate and theliner was laminated to the adhesive-coated sheeting by feeding the linerand the adhesive coated sheeting through two nip rollers.

[0116] The processing conditions were chosen such that theliner/adhesive/substrate exhibited a rating of “1” with respect to theRoll Stability test prior to testing. Rolls of eachliner/adhesive/substrate construction were wound on a core by eitherhand wrapping (“Hand Wrap”) or machine wrapping (“Machine Wrap”),evaluated and rated using the Roll Stability Test Method, as previouslydescribed. The results are reported in Table II. TABLE II Adhesive RollRoll Stability Rating Application Preparation at Test Condition Ex. No.Liner Method Method 150 120/3 120/10 120/22 90/90 Comp. A 5 Direct CoatHand Wrap 5 — — — — Comp. B 3 Liner Hand Wrap 5 — — — — Exchange Ex. 1 2Direct Coat Machine 2-2.5 1   1.5 2 — Wrap Comp. C 6 Liner Machine 4  3.5 5 5 — Exchange Wrap Ex. 2 2 Liner Machine   1.5 1 2 2 — ExchangeWrap Comp. D 6 Liner Machine — — — — 4 Exchange Wrap Ex. 3 2 Direct CoatMachine — — — —   1.5 Wrap Ex. 4 2 Liner Machine — — — — 1 Exchange Wrap

[0117] In general, the severity of roll defects tends to increase withincreasing temperature. Accordingly, if the sample failed at 90° F. (32°C.), for example, one can conclude that the sample will also fail athigher temperatures. The data in TABLE II shows that Liner 2 exhibitedsignificantly better roll stability than Liner 3, Liner 5 or Liner 6 atall test conditions.

Example 5 and Comparative Examples

[0118] The thermal expansion and shrinkage of various liners incomparison to the substrate (Sheeting 3870 with adhesive) were measuredin attempt to correlate such physical properties to the observed rollstability.

[0119] Example 5 (Liner 1 and 2) and the comparative examples (Liners3-6 and Sheeting 3870 with adhesive) were prepared by independentlycutting and testing a sample using the thermal expansion test methoddescribed above.

[0120]FIG. 1 is a plot of L/L₀ (where L is the sample length in mm as afunction of temperature and L₀ is the initial sample length in mm)multiplied by 100 versus temperature in ° C. FIG. 1 shows that Liner 6exhibited a thermal expansion closest to that of Sheeting 3870, yetLiner 6 exhibited poor roll stability, per Table II. Liner 1 and 2,having a thermal expansion less similar to Sheeting 3870 in comparisonto Liner 6, exhibited good roll stability. Accordingly, the data andFIG. 1 show that in contrast to the teachings of WO/14281, there was nocorrelation between thermal expansion and roll stability

[0121] Two samples of each of Sheeting 3870 with adhesive and theindicated liners were prepared for shrinkage evaluation by independentlycutting a sample as described above for thermal expansion measurementtesting. One sample of each was evaluated according to the “ShrinkageTest Method A” as detailed above. A second sample was evaluatedaccording to the “Shrinkage Test Method B” as detailed above.

[0122]FIG. 2 is a plot of the measurements using “Shrinkage Test MethodA”. The figure is a plot of L/L₀ (where L is the sample length in mm ata given time and L₀ is the initial sample length in mm) versus time inminutes.

[0123]FIG. 3 is a plot of the measurements using “Shrinkage Test MethodB”. The figure is a plot of 1−L/L₀ (where L is the sample length in mmat a given time and L₀ is the initial sample length in mm) versus timein days. In FIG. 3, the shrinkage was measured over a longer period oftime than the data plotted in FIG. 2.

[0124] Both FIGS. 2 and 3 show that Liner 1 and 2 exhibited greatershrinkage than Sheeting 3870 with adhesive and Liner 5 and Liner 6exhibited less shrinkage than Sheeting 3870 with adhesive. Accordingly,there is a correlation between shrinkage and roll stability thatdistinguishes Liner 6 from Liners 1 and 2. Based on the shrinkageresults depicted in FIGS. 2 and 3 in combination with the roll stabilityrating reported in Table II, the Applicants concluded that only linershaving a shrinkage greater than or substantially the same as thesubstrate exhibit good roll stability.

Example 6 and Comparative Example E

[0125] Liner 1 and Liner 2 were each independently coated with asolventless acrylate adhesive at a thickness of 0.1 mm (5 mils). Theadhesive coated on Liner 1 was a 93/7 isooctyl acrylate/acrylic acid(“IOA/AA”). The adhesive on Liner 2 was a 95/5 IOA/AA with 12 wt-% of atackifier, commercially available from Hercules, Wilmington, Del. underthe trade designation “Foral 85”. Both adhesives were hot melt coatedonto the liner using a twin screw extruder and a rotary rod die.

[0126] The adhesive surface of each adhesive-coated liner was laminatedto a 0.08 mm thick polyolefin film. The adhesive was crosslinked by EBcuring through the polyolefin film using Model CB 300/45/380commercially available from Energy Sciences, Inc., Wilmington Mass. witha dosage of 3, 6 and 9 Mrads, respectively at 225 Kev.

[0127] The release value of the adhesive from each liner at each EBirradiation dosage was evaluated according to Release Test Method A, aspreviously described, as reported in Table III.

[0128] The data shows that although both Liner 1 and 2 exhibited goodroll stability, Liner 2 exhibits undesirably high release values whenexposed to EB curing. The tackified adhesive used on Liner 2 would beexpected to give higher release numbers than the untackified adhesiveused on Liner 1. However, the results show the significantly lowerrelease values obtained with Liner 2 in spite of the fact that atackified adhesive was used. TABLE III Release Value at EB IrradiationDosage (Mrads) Ex. No. Liner 3 6 9 Comp. E 1 76 126 180 Example 6 2 20 33  43

Examples 7-12 and Comparative Example F

[0129] Examples 7-12 were prepared by coating a silicone composition ona backing. Six silicone compositions were prepared by admixing a vinylterminated polydimethyl siloxane (“PDMS”; VMe₂SiO(SiMe₂O)_(n)SiMe₂V) of(n) value as set out in TABLE IV, a stoichiometric equivalent ofcrosslinker commercially available from Dow Corning Corporation,Midland, Mich. (“Dow”) under the trade designation “Syl-Off 7048”, and50 ppm of platinum catalyst commercially available from Dow under thetrade designation “Syl-Off 7127”.

[0130] The silicone compositions were prepared by the method of siloxanere-equilibration described in U.S. Pat. No. 5,520,978 at Column 8, line38.

[0131] Each release coating composition was coated on a backing that wasa primed polyethylene terephthalate (“PET”) film commercially availablefrom Mitsubishi Polyester, Greer, S.C. under the trade designation“Hostaphan” to provide a release-coated liner construction. Eachrelease-coated liner construction was cured in a 150° C. for 5 minutes,resulting in a dry coating thickness of about 0.5 micrometer.

[0132] A seventh release-coated liner construction was a linercommercially available from Loparex Inc. (formerly Daubert or DCP),Bedford, Ill. under the trade designation “1-803KG-1E”. The releasecoating was a tin catalyzed solvent based silicone composition.

[0133] A 0.1 mm (5 mil) thick adhesive composition consisting of 69% of93/7 IOA/AA and 31% “Foral 85” was coated onto a standard commerciallyavailable silicone release liner. The adhesive on the standard liner wasthen transferred to the release-coated surface of each release-coatedliner construction in TABLE IV by first stripping off the standard linerand then room temperature laminating between two rubber rolls theadhesive to the release-coated liner construction in TABLE IV. Theadhesive on the release-coated liner construction was then cured throughthe exposed adhesive using an EB apparatus commercially available fromEnergy Science Inc., Wilmington, Mass. under the trade designation“Model CB-300” with a dosage of 7 Mrads at 225 Kev.

[0134] Set out below in Table IV are the theoretical degree ofpolymerization ((n) value) of the PDMS, the COF determined using the COFTest Method and the release value measured using Release Test Method B,as described above.

[0135] The data in TABLE IV show that the release-coated linerconstructions of Examples 7-12 in accordance with the present inventionhave a high COF and provide significantly lower release values than therelease-coated liner constructions of Comparative Example F which has alow COF. Upon exposure to EB curing, the adhesive composition ofComparative Example F resulted in a high release value of the liner fromthe adhesive. These test results also explain the findings ofComparative Example E, since Liner 1 was also found to have a high COF,of 0.51, as reported in Table I. TABLE IV (n) Value of Release Ex. No.the PDMS COF Value (g/2.5 cm) Example 7 55 0.8 22.3 Example 8 100 0.631.7 Example 9 200 0.6 — Example 10 470 0.5 42.5 Example 11 900 0.4 69.6Example 12 3300 0.3 154.2 Comp. F ˜5000 0.2 427

Comparative Examples G-P

[0136] The COF of various release-coated liners on commerciallyavailable encapsulated lens retroreflective products was measured. Theliner was removed from the product and the COF measured using the COFTest Method described above, except that the platform of the ModelSP-2000 Slip/Peel Tester was set in motion at a speed of 30.5 cm/min (12in/min) instead of 15 cm/min.

[0137] The data in TABLE V show that all the liners measured had arelatively low COF, namely 0.24 or less. Thus, these liners employed oncommercially available sheeting would be expected to exhibitunacceptably high release values upon removal of the liner from anadhesive that had been EB cured. TABLE V Retroreflective Sheeting TradeEx. No. (Manufacturer) Designation COF Comp. G American Traffic SafetyMarketing “3824 II” 0.21 Inc. (Orange Park, FL) Comp. H Lucky Gold Star(Seoul, Korea) “8000 Series 0.22 White” Comp. I Lucky Gold Star (Seoul,Korea) “8000 Series 0.23 Blue” Comp. J Nippon Carbide Industries Company“800-12” 0.16 Incorporated (Tochigig-ken, Japan) Comp. K Nippon CarbideIndustries Company “800-4” 0.14 Incorporated (Tochigig-ken, Japan) Comp.L Lucky Gold Star “8000 Series 0.21 Red” Comp. M Lucky Gold Star “8000Series 0.24 Green” Comp. N Lucky Gold Star “8000 Series 0.21 YellowComp. O Kiwa Chemical Industry Company “22013 White” 0.14 Ltd.(Wakayame, Japan) Comp. P American Traffic Safety Marketing “3870” 0.23Inc.

What is claimed is:
 1. An article comprising an adhesive layer disposedbetween a substrate and a liner, the liner having an adhesive-facingsurface releasably adhered to the adhesive; wherein the adhesive-facingsurface has a coefficient of friction of at least about 0.30; thesubstrate exhibits shrinkage; and the liner exhibits shrinkage rangingfrom substantially the same as to greater than the substrate.
 2. Thearticle of claim 1 wherein said article exhibits good roll stability. 3.The article of claim 1 wherein the substrate has a force per unit widthof at least two to three times greater than the liner.
 4. The article ofclaim 1 wherein the substrate has a force per unit width of at least1×10³ Newtons/cm greater than the liner.
 5. The article of claim 1wherein the substrate has a force per unit width of at least 1×10⁴Newtons/cm greater than the liner.
 6. The article of claim 1 wherein thecoefficient of friction is at least about 0.40.
 7. The article of claim1 wherein the coefficient of friction is at least about 0.45.
 8. Thearticle of claim 1 wherein the coefficient of friction is at least about0.50.
 9. The article of claim 1 wherein the substrate comprises acrylic,poly(vinyl chloride), poly(vinyl fluoride), polyurethane, polyolefin,polyester, and combinations thereof.
 10. The article of claim 9 whereinthe substrate comprises acrylic or polyolefin.
 11. The article of claim1 wherein the adhesive is a heat-stable.
 12. The article of claim 1wherein the adhesive is crosslinked.
 13. The article of claim 1 whereinthe adhesive is acrylate based.
 14. The article of claim 1 wherein saidadhesive is substantially free of photoinitiator.
 15. The article ofclaim 1 wherein the substrate is retroreflective sheeting.
 16. Thearticle of claim 15 wherein the retroreflective sheeting comprisespolymethylmethacrylate.
 17. The article of claim 15 wherein theretroreflective sheeting comprises an enclosed-lens, an encapsulatedlens, or cube-corner construction.
 18. The article of claim 15 whereinthe retroreflective sheeting comprises an encapsulated lensconstruction.
 19. The article of claim 1 wherein the release linercomprises a backing and a release coating compositions on saidadhesive-facing surface wherein said release coating compositioncomprises a cure-on-demand moisture curable composition having reactivesilane functionality.
 20. The article of claim 19 wherein themoisture-curable compositions comprises a compound comprising moleculesbearing reactive silane functional groups and an acid generatingmaterial that is free of ammonium salt.
 21. An article comprising asubstrate having an encapsulated lens retroreflective viewing surfaceand an opposing surface, an adhesive layer disposed between saidopposing surface of the substrate and a liner, and the liner having anadhesive-facing surface releasably adhered to said adhesive; wherein theadhesive-facing surface of the liner has a coefficient of friction of atleast about 0.30.
 22. The article of claim 21 wherein the substrateexhibits shrinkage.
 23. The article of claim 21 wherein the linerexhibits shrinkage ranging from substantially the same as the substrateto greater than the substrate.
 24. The article of claim 21 wherein thesubstrate comprises polymethylmethacrylate.
 25. The article of claim 21wherein the adhesive is a heat-stable.
 26. The article of claim 21wherein the adhesive is crosslinked.
 27. The article of claim 21 whereinthe adhesive is acrylate based.
 28. The article of claim 21 wherein saidadhesive is substantially free of photoinitiator.
 29. A method of makingan article comprising: a) providing a substrate that exhibits shrinkage;b) providing a liner that exhibits shrinkage ranging from substantiallythe same as the substrate to greater than the substrate and acoefficient of friction of greater than 0.30; c) coating the substratewith an adhesive composition; d) contacting the liner to the adhesivecomposition forming an article; and e) winding the article into a roll.30. The method of claim 29 wherein said article exhibits good rollstability.
 31. The method of claim 29 wherein the substrate isretroreflective
 32. The method of claim 29 further comprising exposingthe adhesive to an electron beam energy source.
 33. A method of makingan article comprising: a) providing a substrate that exhibits shrinkage;b) providing a liner that exhibits shrinkage ranging from substantiallythe same as the substrate to greater than the substrate and acoefficient of friction of greater than 0.30; c) coating the liner withan adhesive composition; d) contacting the substrate to the adhesivecomposition forming an article; and e) winding the article into a roll.34. The method of claim 33 wherein said article exhibits good rollstability.
 35. The method of claim 33 wherein the substrate isretroreflective.
 36. The method of claim 33 further comprising exposingthe adhesive to an electron beam energy source.
 37. A method of makingan article comprising: a) providing a substrate that exhibits shrinkage;b) providing a first liner; c) coating the first liner with an adhesivecomposition; d) contacting the substrate to the adhesive composition; e)stripping the first liner exposing the adhesive; f) contacting theadhesive to a second liner that exhibits shrinkage ranging fromsubstantially the same as the substrate to greater than the substrateand a coefficient of friction of greater than 0.30 forming an article;and g) winding the article into a roll.
 38. The method of claim 37wherein said article exhibits good roll stability.
 39. The method ofclaim 37 wherein the substrate is retroreflective.
 40. The method ofclaim 37 further comprising exposing the adhesive to an electron beamenergy source.